1. Field of the Invention
The present invention relates generally to a display device and method for driving the same, and more particularly, to a display device which compensates for degradation of threshold voltage of a driving thin-film transistor and a method for driving the same.
2. Description of the Related Art
Presently, many efforts are being made to study and develop various types of flat panel display devices, such as liquid crystal displays (“LCDs”), field emission displays (“FEDs”), organic light emitting diodes (“OLEDs”) and plasma display panels (“PDPs”).
An organic light emitting display device is a self-emissive display that displays an image by electrically exciting a fluorescent organic material. The organic light emitting display device offers several advantages including low power consumption, wide viewing angle, fast response time, and so on, thereby facilitating a high quality moving image display.
An organic light emitting display device includes an OLED and a thin-film transistor (“TFT”) for driving the same. TFTs are classified into polycrystalline silicon TFTs and amorphous TFTs depending on the type of active layer used.
An organic light emitting display device using amorphous TFTs can easily achieve a large display size. However, use of amorphous TFTs for more than a predetermined time may degrade and change a threshold voltage Vth of the amorphous TFTs. Degradation of the threshold voltage Vth may prevent uniform current flow through the OLED even though the same data voltage is applied to the organic light emitting display device, thus degrading the image display quality of the organic light emitting display device.
Meanwhile, an organic light emitting display device exhibits a change in the threshold voltage as current flows over a long period of time. For example, it is assumed that an organic light emitting display device is connected to a source of an n-channel metal oxide semiconductor (“n-MOS”) TFT. In any event where a threshold voltage of the organic light emitting display device deteriorates, a source voltage of a driving TFT inevitably changes. Accordingly, even if the same voltage is applied to the gate of the TFT, non-uniform current flows through the OLED due to a change in the gate-source voltage of the TFT, thereby resulting in degradation of the image display quality of the organic light emitting display device.